Project Summary/Abstract From 2012 to 2016, the number of people living with HIV in the US whose infection is attributable to male- to-male sexual contact increased from 462,027 to 542,000 and, at year-end 2016, these men comprised 55% of the HIV-positive population. Continued education about HIV transmission risk and prevention strategies among men and transgender people who have sex with men (MTSM) is crucial. In recent years, treatment as prevention (TasP) has emerged as an effective HIV prevention strategy that could have multiple benefits to the public health. In light of clinic trial evidence, the CDC now states, ?People with HIV who take HIV medicine as prescribed and get and keep an undetectable viral load have effectively no risk of transmitting HIV to their HIV- negative sexual partners.? Making HIV-positive people practically noninfectious, TasP represents an important tool not only for reducing HIV incidence but also for fighting HIV-related stigma and improving the well-being of HIV-positive people. However, TasP will only fulfill its promises if people accept it as an effective and reliable prevention strategy. Unfortunately, the most recent data show that although there seems to be high awareness of TasP among MTSM, few seem to believe in its efficacy or to be willing to use it. This study will use the Precaution Adoption Process Model (PAPM) to investigate the factors associated with different stages of TasP adoption among men and transgender people who have sex with men (MTSM). We will conduct in-depth qualitative interviews with 60?75 MTSM in the US, divided between HIV-positive and HIV-negative/unaware individuals not using PrEP. We will focus on three positions regarding TasP adoption that we have found to be common in our preliminary data and that map onto key stages in the PAPM: TasP skeptics (who do not believe in the effectiveness of TasP), TasP believers (who understand TasP is effective but are not willing to rely on it), and TasP adopters (those who have relied on the strategy). The screening survey we will use to recruit interview participants will provide further data about other stages of TasP adoption (awareness, perceived effectiveness, willingness to use, and actual use) in a larger and more diverse sample of participants (including PrEP users). The specific aims are: 1. To examine (with qualitative interview data) factors associated with MTSM?s perceived effectiveness of TasP and their willingness to rely on it. 2. To understand (with qualitative interview data) the experiences of MTSM who use TasP, how they use the strategy, and how it affects their sexual behaviors and decisions. 3. To describe (with screener survey data) the characteristics of MTSM at different stages of TasP adoption (awareness, perceived effectiveness, willingness to use, and actual use). 4. To begin development of an intervention to correct misconceptions about TasP, overcome barriers to its use, and educate MTSM on how to most effectively use the prevention strategy.